In the motion picture industry, it is common practice to make prints of a duplicate motion picture negative. This is done for several reasons, the most significant being that the original negative is preserved as a master record. Thus, typically, the original negative is copied onto an intermediate negative film one or more times. That copy, in turn, is used to make positive prints which are projected in a movie theatre.
Copying of the original negative record to make an intermediate negative, or printing of an intermediate negative record to give a positive is accomplished by illuminating the record to be copied with a lamp so that radiation passing thru the record to be copied impinges on the light sensitive material in which the reproduction will be formed.
It is common practice to employ as the source of illumination three separate portions of the visible spectrum; one which has its peak in the blue region of the spectrum, between about 400 and 500 nm, one which has its peak in the green region of the visible spectrum between about 500 and 600 nm, and one which has its peak in the red region of the visible spectrum between about 600 and 700 nm. The exposing radiation could be provided by three separate light sources of the appropriate spectral distribution, or it could be provided by a single white light source which is split into three separate beams which are filtered with red, green or blue filters before they illuminate the record being copied. Typically each of the exposure sources, the dyes which provide the absorption in the record to be copied and the sensitivity of the light sensitive element onto which the copy is made are chosen so that their peaks approximately match.
The type of exposure source described above is referred to in the art as an additive lamp house. While it is the one which is commonly used in the motion picture industry for reproduction of negatives and preparation of prints, it is not the only one which is used. Also known are light sources which have a continuous emission across the visible region of the spectrum. These are commonly referred to as subtractive light sources or as subtractive lamp houses. When an original record to be copied is exposed to such a light source, it modulates the light differently than it does light from an additive light source and, as a result, the spectral wavelength distribution of the light reaching the light sensitive material and, consequently, the color reproduction in the copy are different. This can be a problem, especially when reproductions exposed with both types of light source are ultimately joined in a single print.
Heretofore the industry has used two separate types of reproduction material, one for additive light sources and one for subtractive light sources. This has associated with it all of the problems associated with multiple inventories.
We have found that selective filtration with narrow band filters modifies the light modulated by the record being copied and can result in a reproduction using an subtractive light source that is compatible with a reproduction made using an additive light source.
While narrow band filters have been used previously to modify reproductions, they have been used in different ways and for different purposes than they are used in accordance with the present invention.
Hehn U.S. Pat. No. 3,085,468, issued Apr. 16, 1963 describes the use of dichroic filters in printing photographic originals in place of the red, green and blue filters commonly used in additive printing systems.
Krause U.S. Pat. No. 4,359,280, issued Nov. 16, 1982 describes the use of dichroic filters, and other narrow band filters to modify contrast by shifting peak intensity characteristics of the light modulated by the record being copied. This is different from the present invention in which the peak intensities are not changed.